1. Field of the Invention
The present invention relates to a hybrid construction machine using engine power and stored electrical power of an electrical energy storage device in combination.
2. Description of the Related Art
Hybrid construction machinery is classified into a series type and a parallel type in accordance with the way of using engine power and stored electrical power. An example of the parallel type is disclosed in Japanese Unexamined Patent Application Publication No. 2004-150305.
In a common hydraulic shovel, which is not based on a hybrid mode, its engine sound varies depending on the magnitude of a workload. Usually, an operator estimates the workload by listening to the engine sound, and feeds back the estimated result to the operation of the hydraulic shovel. For example, if the operator estimates that the load is large, he/she performs an operation in a direction reducing the load.
Surrounding workers recognize, at the engine sound, that the machine is operating, and take caution.
That is, in the construction machine, its engine sound constitutes information that is important for the operator and surrounding workers, from the aspects of safety and operation.
In the hybrid system, both of the series and parallel types are configured so that, basically, an electrical energy storage device compensates for a shortage of an engine output. As a result, while the hybrid system is operating, the engine sound does not change, or little changes in spite of changes in the workload. In other words, the engine sound, which serves as operation information, is not conveyed to the operator.
This makes it impossible to estimate the load, and hence, the above-described conventional way of feeding back the engine sound to operations cannot be used. In addition, the operator develops an illusion that the load is small, or the machine itself is lacking in power. This incurs a reduction in work efficiency.
On the other hand, in the series type, as will be described later, when preset engine stop conditions (a small load as well as a large amount of charge) have been satisfied, the engine is automatically stopped, and the construction machine automatically transfers to a state of performing the operation by its stored electrical power alone without using the engine. Thus the engine sound disappears.
As a result, especially surrounding workers might not notice that the machine is operating.
A technique for preventing surrounding workers from the machine is disclosed in the above-described Japanese Unexamined Patent Application Publication No. 2004-150305.
According to this technique, in the parallel type, from the viewpoint of energy saving, the engine is configured so as to be automatically stopped when an operation lever is put into its neutral position, and restarted upon operation of the lever. On that premise, when the lever is in the neutral position, the machine is arranged to issue an alarm indicating that “upon operation of the lever, the machine starts to move”, for alerting surrounding workers.
The reason why the alarm is issued only when the lever is in the neutral position and no alarm is issued when the lever is operated, is because, when the lever is operated, the engine moves without fail and the workers can recognize, at that engine sound, that the machine is operating.
However, in the series type, there exists a specific situation of “operation without using the engine” wherein, if given conditions have been satisfied, the engine is stopped irrespective of the presence/absence of a lever operation, and the machine moves under stored electrical power even during engine stop, this situation existing in common construction machinery and parallel typed hybrid construction machinery. For this reason, if the known technique in which no alarm is issued during the operation of lever is diverted toward the series type just as it is, the safety of workers cannot be ensured.
In other words, in the series type, it is the lever operating period during which the machine is moving without an engine sound that poses a danger to the workers. Nevertheless, this technique cannot address this problem. Worse still, there is a possibility that workers will confuse a non-alarm state with safety, resulting in an even more significant danger.
In this manner, in the conventional construction machinery, there have been occurred inherent problems based on that the information that the construction machine is in operation, and the engine sound information indicating the magnitude of a workload are not conveyed to the operator or surrounding workers, or not correctly conveyed to them.
As an example of the series type, Japanese Unexamined Patent Application Publication No. 2000-283107 discloses a series type hybrid system. In this system, with at least one value out of a workload and the charge amount of an electrical energy storage device as a determining factor, when the value has reached an engine stop set value, the engine is automatically stopped, and an operation is performed by only stored electrical power of the electrical energy storage device without using the engine. Then, when the values of the above-described determining factors have reached the engine restart set values, the engine is automatically restarted.
To explain it with reference to a typical instance:    (i) when the conditions that the workload value is a set value or less (small load) and simultaneously the charge amount of an electrical energy storage device is a set value or more (large charge amount; for example, 65% or more of the full charge state) have been satisfied, the engine is automatically stopped, and the hybrid system is transferred to an operating state without using the engine, with the motor driven by stored electrical power alone.    (ii) during this operation without using the engine, when the workload value has become higher than the set value, or the charge amount has become lower than the set value (small charge amount; for example, lower than 50% of the full charge state), the hybrid system is controlled to return to the hybrid operation by automatically restarting the engine.
Thereby, the hybrid system is intended to stably operate the engine in a high efficiency region, and perform an energy-saving operation by causing the electrical energy storage device to compensate for a shortage of an engine output with respect to the workload, while keeping the charge amount of the electrical energy storage device within a fixed range.
However, the transfer from the operation without using the engine to the engine restarting was automatically executed irrespective of an intention of the operator. Such an abrupt engine restart has taken the operator and surrounding workers by surprise, and has been detrimental to their mental health.
Also, the engine restart in the progress of performing a fine operation with the operator's attention concentrated thereon, might disturb the operator to thereby cause him/her to miss aim, thereby exerting a harmful effect on work efficiency. An improvement in this respect has therefore been required.